In recent years, silicone hydrogel contact lenses become more and more popular because of corneal health benefits provided by their high oxygen permeability and comfort. Although various methods have been disclosed to make colored non-silicone hydrogel contact lenses (see, for example, disclosed in U.S. Pat. Nos. 4,668,240, 4,857,072, 5,272,010, and 5,414,477 and U.S. Patent Application publication Nos. 2003/0054109, 2004/0044099, 2005/0221105, 2006/0065138, and 2006/0077341, all of which are incorporated herein by reference), only a few methods (see, e.g., co-pending U.S. Patent Application Nos. 2005/0237483 and 2006/0055882) have been developed for making colored silicone hydrogels contact lenses which can enhance the natural beauty of the eye.
However, there are some limitations associated with the inks disclosed in those co-pending patent applications. For example, those inks may not be well suitable for making colored silicone hydrogel contact lenses based on a print-on-mold process, in which colored contact lenses can be produced by printing inks on molds, curing the inks, filling the molds with lens formulation, closing mold assemblies and finally curing the lens in the molds. Unlike non-silicone hydrogel lens formulations, silicone hydrogel lens formulations contain organic solvent, monomers, or both thereof, which have high solvating capability. Once the cured inks or partially cured inks on a mold are exposed to a lens formulation, the cured or partially cured inks may be solvated by some monomers and solvent in the lens formulation. Since the cured ink can be soaked in the lens formulation inevitably for a relatively long period of time in the manufacturing environment (e.g., such as, line stoppage or line staging operations), the cured ink may become fragile. As such, the printed image on the mold may be susceptible to damages as excess lens formulation is sheared across it during mold closing and therefore can compromise the quality of printed images. It is desirable that, during the production of colored silicone hydrogel contact lenses by a print-on-mold process, ink prints cured on molds are durable even if it is soaked in a lens formulation prior to closing molds and curing the lens formulation.
In addition, during the manufacture of silicone hydrogel contact lenses it is often necessary and or desirable to extract lenses with organic solvent (e.g. methanol, ethanol, isopropanol). During extraction in organic solvent, lens dimensions often increase substantially as compared to lens dimensions in water. The lens extraction in organic solvent is often followed by extraction in water and equilibration in saline. Therefore there is a need for silicone hydrogel binder polymers and ink systems that can withstand large and substantially reversible dimensional changes as colored silicone hydrogel lenses are extracted in organic solvent and water. If the cured ink is too weak it might rupture and the print pattern could be damaged. It is therefore important to have a means to influence or adjust expansion characteristics of cured inks (or binder polymers) in both organic and water solvents.
Therefore, there exist needs for methods of making colored silicone hydrogel contact lenses, and for inks suitable for making colored silicone-hydrogel lenses with high-quality color images thereon.